1. Through this retrospective study, researchers found that 0.42% of study infants undergoing CSF culture for suspected meningitis tested positive for herpes simplex virus (HSV) infection. HSV infection was more common in infants aged 1-4 weeks when compared to infants from age 5-9 weeks.

2. Across the 23 study sites, there was wide practice variation in the approach to testing and empiric acyclovir treatment of neonatal HSV.

Study Rundown: Neonatal HSV infection can lead to serious morbidity and mortality if not promptly diagnosed and treated. Currently, there is limited data on the probability of HSV infection in neonates with suspected meningitis, and few evidence-based guidelines on the evaluation and empiric treatment of HSV exist. In the current study, researchers examined the medical records of infants undergoing lumbar puncture to evaluate for meningitis in 23 North American Emergency Departments (EDs). Among those evaluated, HSV infection, whether of skin, central nervous system, or disseminated, was identified in only 0.42% of study patients. Positive results were more likely in in younger infants (1-4 weeks compared to 5-9 weeks). Researchers also examined secondary outcomes including when HSV testing was performed and when empiric acyclovir treatment was initiated, and found large variation by study site. The major limitations of this study included assuming infants not tested for HSV were uninfected, as well as between site variation in lab work-up of patients. However, the data provide an important context for developing evidence-based guidelines in the diagnosis and treatment of HSV infection in infants.

In-Depth [retrospective cohort]: Medical records from 26 533 ED encounters with 26 102 unique patients were included in this study. Of those encounters, 51.6% were of infants less than 28 days old. Encounters were included if an infant who presented to the ED underwent cerebrospinal fluid (CSF) sampling to evaluate for potential meningitis. The primary outcome measured was the proportion of included encounters where HSV infection was identified by positive polymerase chain reaction or viral culture from CSF, blood or surface swabs. HSV infection was identified in 0.42% (95%CI: 0.35-0.51) of included encounters. HSV was more frequently identified in encounters with infants aged 0 to 28 days when compared to infants 29-60 days old (OR: 3.9, 95%CI: 2.4-6.2). Significant variability was found in the frequency with which site EDs performed HSV testing with 34.6% of encounters including testing (range: 14.4-72.1, p < 0.001). There was also significant between-site variation in those empirically treated for HSV, with 23.4% receiving empiric treatment overall range 4.2%-53%, p < .001). Based on the frequency of identified HSV infection in study infants, the number needed to treat with empiric acyclovir was 237.